Current forecast models from Brazil’s INMET and international ensembles like ECMWF indicate a highest temperature near 18–19 °C for São Paulo on May 19, driven by persistent cool advection behind a recent cold front and increased cloud cover that limits daytime heating. This aligns with the market’s leading 18 °C outcome at 31.5 % implied probability while the broad distribution across 16–20 °C reflects remaining uncertainty in exact frontal timing and subtropical moisture return. Historical May climatology shows average highs near 22 °C, so the current cooler pattern represents a notable deviation that traders are pricing in. Updated 48-hour model guidance and INMET’s next official bulletin are the key near-term data releases that could shift probabilities toward 17 °C or 20 °C if steering winds or insolation change.